1. Field of the Invention
The present invention relates to a backlight unit and a method for fabricating the same. More particularly the present invention relates to a direct type backlight unit and a method for forming a diffuser in the direct type backlight unit, in which a structure of a diffuser or a diffusion sheet is improved to prevent a mura of a lamp from occurring.
2. Discussion of the Related Art
A liquid crystal display (hereinafter, referred to as “LCD”) device has been widely used as a flat panel display device. Since such an LCD device is a passive display device that does not emit light by itself, the LCD device is provided with a backlight unit on a rear surface of an LCD panel as a light source to display images. Accordingly, the LCD device is affected by a structure of the backlight unit. The backlight unit is divided into an edge type and a direct type based upon the position of a light source with respect to a display area. The edge type backlight unit requires a light guide plate that changes linear light of a lamp to surface light as the lamp is arranged laterally. The direct type backlight unit does not require a light guide plate because the lamp is arranged below a display area. The direct type backlight unit is widely used for large sized LCD devices because the light efficiency is high, the configuration is simple, and there is no limitation in size of the display area.
As shown in FIG. 1 and FIG. 2, the direct type backlight unit includes a plurality of lamps 13 arranged below a display area, a reflecting plate 11 reflecting light emitted from the lamps 13 toward the display area to prevent light loss from occurring, a diffuser 15 and a diffusion sheet 17 diffusing the light from the top of the lamps 13 to uniformly emit the light, and a prism sheet 19 condensing the light, which is diffused to the contour, on the center to improve luminance at the front of the panel. The diffuser 15, the diffusion sheet 17 and the prism sheet 19 are sequentially arranged above the lamps 13. The prism sheet 19 includes a transparent resin 19a and a plurality of triangular prisms 19b arranged on the transparent resin 19a. 
In the direct type backlight unit, because the lamps are arranged on the plane, their shapes are displayed in the LCD panel, whereby the distance between the lamps and the LCD panel is considerable concern. For this reason, problems occur in that there is a limitation in forming a thin sized LCD device and an imbalance of luminance is caused in the panel. In other words, since the lamps 13 are arranged below the display area, light density on the rear surface of the diffuser 15 arranged vertically to the lamps 13 varies from light density on the rear surface of the diffuser arranged between the lamps 13, whereby imbalance of luminance is caused.
Accordingly, to solve the above problems, in the related art direct type backlight unit, the reflecting plate 11 having a triangular prism pattern 11a is used as shown in FIG. 1 and FIG. 2.
The direct type backlight unit is provided with a plurality of a triangular prism patterns 11a formed on the reflecting plate 11. The prism patterns 11a are arranged between the lamps 13 and reflect the light toward the display area to minimize loss of the light. In other words, the prism patterns 11a reduce a dark portion between the lamps 13 to minimize luminance deviation.
However, as described above, to form the prism patterns on the reflecting plate, the reflecting plate that can be processed is required. In other words, the reflecting plate is processed using a separate pressing material to form the prism patterns. In this case, the material cost increases as the reflecting plate is processed, and the backlight unit has an increased weight as the separate pressing material is used. Also, since water variation of the shape display of the lamps on the LCD panel seriously occurs due to peak portions of the prism patterns, stability in mass production is reduced.